It is common to burn a mixture of containment gases (gases within the housing surrounding a nuclear reactor) containing hydrogen and air from nuclear power plants by passing said gaseous mixture through a hydrogen recombiner wherein said gaseous mixture is heated to its ignition temperature to convert, by oxidation, the hydrogen therein to water before discharging the resulting recombined gases from the hydrogen recombiner. When the hydrogen content of the containment gases is small, for example, up to about 4 volume percent, the conversion of hydrogen to water results in an increase in the temperature of the resulting recombined gases further above the ignition temperature of the containment gases. However, by the time the resulting recombined gases are discharged from the hydrogen recombiner, the temperature thereof has normally fallen below the ignition temperature of the containment gases. Therefore, there is no chance that the resulting recombined gases upon discharge from the hydrogen recombiner will give rise to spontaneous combustion of containment gases external of the hydrogen recombiner. However, in the event the concentration of hydrogen in the containment gases continues to rise above about 4 volume percent, for example, upwardly to about 8 to 10 volume percent, burning of such gases in the hydrogen recombiner to convert all of the hydrogen therein to water vapor will result in steadily increasing temperatures of the resultant recombined gases substantially above the ignition temperature of the containment gases. Even though the temperature of the latter resultant recombined gases may still be cooled somewhat before discharge from the hydrogen recombiner, the temperature thereof will still be in excess of the ignition temperature of the containment gases. Therefore, when they are discharged from the hydrogen recombiner, the will give rise to spontaneous combustion of containment gases external of the hydrogen recombiner.
We have found that the above difficulties can be overcome, even when mixtures of containment gases containing up to about 8 to 10 volume percent hydrogen are burned in a hydrogen recombiner and the recombined gases have a temperature in excess of their ignition temperature prior to discharge from the hydrogen recombiner, by cooling the exit gases to a temperature level below their ignition temperature after said burning but before discharging them from the hydrogen recombiner. Our discovery also relates to apparatus for obtaining the above results.